<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>observe</title>
</head>
<body>
  <div id="app">
    {{ arr }}
  </div>

  <script src="../../dist/vue.js"></script>
  <script>
    const vm = new Vue({
      el: '#app',
      data: {
        arr: [2, 3, 5]
      }
    })

    // vm.arr.push(8)
    // vm.arr[0] = 100
    // vm.arr.length = 0
    
  </script>
</body>
</html>